Considers the process of neurotransmission, especially chemicals used in the brain and elsewhere to carry signals from nerve terminals to the structures they innervate. Focuses on monoamine transmitters (acetylcholine; serotonin; dopamine and norepinephrine); also examines amino acid and peptide transmitters and neuromodulators like adenosine. Macromolecules that mediate neurotransmitter synthesis, release, inactivation, and receptor-mediated actions are discussed, as well as factors that regulate their activity and the second-messenger systems they control. Alternate years.